A fuel cell using a solid polymer electrolyte in the related art is a device that allows a fuel gas containing hydrogen and an oxidant gas such as air containing oxygen to electrochemically react with each other and generates power and heat at the same time. The fuel cell includes a stacked body of a unit cell called a fuel battery cell. As shown in FIG. 1, a general fuel cell includes a stacked body 14 in which 10 to 200 fuel battery cells are stacked, and includes a pair of current collector plates 9 between which both ends of the stacked body 14 are interposed, insulation plates 10 between which the pair of current collector plates 9 are interposed, and a pipe-attached end plate 11. Examples of a pipe of the pipe-attached end plate 11 include a pipe that supplies a reaction gas, a pipe that supplies a cooling liquid, and the like. In addition, a fuel cell stack is fastened with a bolt 12 and a nut 13.
The fuel battery cell of the fuel cell using the solid polymer electrolyte includes a polymer electrolyte membrane that selectively conveys hydrogen ions, and a pair of electrodes between which the polymer electrolyte membrane is interposed. Each of the electrodes includes a catalyst layer that contains a carbon powder that supports a platinum group metallic catalyst as a main component, a gas diffusion layer that is formed outside the catalyst layer and has both gas permeability and electronic conductivity.
A gas sealing material or a gasket, which prevents the fuel gas and the oxidant gas that are supplied from leaking to the outside or prevents the fuel gas and the oxidant gas from being mixed with each other, is disposed on the periphery of the electrodes of the fuel battery cell with the polymer electrolyte interposed therebetween. The sealing material or gasket, the electrodes, and the polymer electrode membrane may be integrated and assembled in advance. This assembly is called an MEA (electrolyte membrane electrode assembly).
A fuel battery cell includes conductive separators that are disposed at both surfaces of the MEA. The conductive separator mechanically fixes the MEA and electrically connects adjacent MEAs in series. A flow channel, which supplies a reaction gas (a fuel gas or an oxidant gas) to an electrode surface and carries away generated water or excess gas, is formed at a portion at which the separator and the MEA come into contact with each other. Generally, this flow channel is constructed by a groove formed at a contact surface of the separator and the MEA, but may be provided as a member that is separate from the separator.
The fuel cell generates heat during operation, and thus it is necessary for the fuel cell to be cooled down with a cooling liquid so as to approximately maintain a temperature state of the fuel battery cell. Accordingly, at least a part of fuel battery cells of the fuel cell is provided with a cooling portion through which the cooling liquid flows. The cooling portion may be provided to all of the fuel battery cells, but may be provided every one to three fuel battery cells. The cooling portion may be constructed by a cooling liquid flow channel member that is interposed between the fuel battery cells. However, in many cases, the cooling portion is a cooling liquid flow channel that is provided to the separator of the fuel battery cell on a surface opposite to the contact surface with the MEA.
FIG. 2A shows a stacked cross-section in the vicinity of a cooling liquid manifold 5 of a general fuel cell in the related art, and FIG. 2B shows a perspective diagram in the vicinity of the cooling liquid manifold 5. In FIGS. 2A and 2B, a fuel battery cell 6, which includes a frame 1 that is integrated with MEA 1-a, an anode separator 2, and a cathode separator 3, is shown. A fuel gas flow channel 2a through which a fuel gas flows is provided to the anode separator 2 in a surface that comes into contact with the MEA 1-a, and an oxidant gas flow channel 3a through which an oxidant gas flows is provided to the cathode separator 3 in a surface that comes into contact with the MEA 1-a. Furthermore, a cooling liquid flow channel 7 is provided to the cathode separator 3 in a surface opposite to the surface that comes into contact with the MEA 1-a. 
Furthermore, a cooling liquid flows through the cooling liquid manifold 5 that penetrates through the frame 1, the anode separator 2, and the cathode separator 3. The cooling liquid flows along a lamination direction (an arrow X-X) of the fuel battery cells. In addition, a flow channel cross-sectional area (an area of a cross-section orthogonal to a flow direction of the cooling liquid) of the cooling liquid manifold 5 is expressed by a diagonal line region a and the area thereof is constant.
As described above, the fuel cell includes a stacked body of fuel battery cells. However, in the fuel battery cells that are connected to each other in series, it is necessary for contact resistance between adjacent fuel battery cells to be suppressed as low as possible so as to suppress ohmic loss during power generation.
On the other hand, it is necessary to reliably form insulation between an anode and a cathode constituting each of the fuel battery cells. In addition, it is necessary to make the resistance between battery cells that are not adjacent to each other, rather than battery cells that are adjacent to each other, as large as possible and to maintain the insulation state. In a case where members which should be insulated from each other are short-circuited by a material such as a metal having high electronic conductivity, since a current corresponding to a resistance flows, power that should be supplied to the outside of the fuel cell is consumed inside the fuel cell, and thus the power generation efficiency decreases.
In addition, members which should be insulated from each other may be short-circuited due to an ion conductor such as tap water. When the short-circuit due to the ion conductor occurs, an oxidation reaction occurs at an interface between a high-voltage side battery cell and the ion conductor while a current flows to the ion conductor. As a result, corrosion degradation of a constituent member of the fuel battery cell occurs. Finally, this may lead to a leakage of the fuel gas or the cooling liquid to the outside of the fuel cell.
As shown in FIGS. 2A and 2B, in a fuel cell having a general construction, the cooling liquid that flows through the cooling liquid manifold 5 comes into contact with a plurality of fuel battery cells. Accordingly, so as to suppress a decrease in the above-described power generation efficiency or corrosion deterioration, it is necessary to maintain the insulation state by using pure water as the cooling liquid.
However, during power generation of the fuel cell, an ion component, which elutes from a pipe member that comes into contact with the cooling liquid or a material such as a metal and a resin that is used in the fuel cell, or carbon dioxide gas, a NOx gas, an SOx gas, or the like in the air is dissolved in the cooling liquid. Accordingly, even when the cooling liquid is formed from pure water, conductivity of the cooling liquid gradually increases. So as to maintain the conductivity of the cooling liquid to be low, the purity of the cooling liquid may be raised, the cooling liquid may be purified by an ion exchange resin, or pure water may be additionally added to the cooling liquid so as to dilute the cooling liquid. However, when carrying this out, an increase in the scale of a system due to an increase in incidental equipment or cost increases in direct material costs, maintenance costs, or the like become problematic.
Therefore, a technology in which a current (corrosion current) flowing through the cooling liquid inside the cooling liquid manifold is suppressed by partially narrowing a flow channel cross-sectional area of the cooling liquid manifold without making the flow channel cross-sectional area constant is suggested (refer to Patent Document 1).
In addition, devising of a shape of the flow channel of the manifold into various kinds of shapes is suggested. For example, a technology in which a protrusion or a bridge part is provided inside the gas manifold to adjust the gas flow is suggested (Patent Documents 2 and 3). In addition, a technology in which a plate that blocks the gas flow is provided in the vicinity of a supply port inside the gas manifold or the cooling liquid manifold to make the gas flow or the cooling liquid flow have a spiral shape is suggested (Patent Documents 4 and 5). In addition, a technology in which the flow channel is made to have a spiral pin shape so as to promote discharge of a liquid that is generated in an off-gas manifold is suggested (Patent Document 6). In addition, a technology in which a flow channel of the cooling liquid manifold attached to the outside of a stacked body is made to have a spiral shape is suggested (Patent Document 7). In addition, a technology in which an inner portion is provided on an inner circumferential surface of a core (manifold) formed from a metal to suppress corrosion of a metal making up the core is suggested (Patent Document 8).
In addition, a fuel cell separator, which includes a conductive flow channel portion and an insulating periphery surrounding the conductive flow channel portion, and in which a manifold is provided to the insulating periphery is suggested (Patent Document 9).